A review of 1,236 patients admitted to The Mount Sinai Hospital with inflammatory bowel disease between 1960 and 1979 yielded 75 cases (6%) with toxic dilatation of the colon. There were 61 cases among 613 patients (10%) with ulcerative colitis (UC), and 14 of 623 (2.3%) with Crohn's disease (CD). Fifty-nine of the 75 patients (79%) underwent surgery during their hospitalization with toxic dilatation. Twelve of the 75 patients (16%) died. Both UC and CD groups had similar mean ages at onset of colitis (32 years and 31 years, respectively) and at development of toxic dilatation (37 years); similar durations of overall disease (4.8 and 5.9 years) and of toxic dilatation prior to surgery (11 days and 13 days); and similar anatomic distributions of disease. Both UC and CD also had similar mortality rates (16% and 14%). Mean duration of presenting attack up to onset of toxic megacolon was longer in CD than in UC (62 days versus 31 days) and in unoperated versus operated cases (64 days versus 37 days), but was not significantly different between survivors and mortalities (43 days versus 39 days). Mortality rates were also unaffected by total duration of inflammatory bowel disease, first attack versus relapse (14% versus 18%), or medical versus surgical therapy (13% versus 17%). Factors which affected mortality included age (30% for patients over 40 years old, versus 5% for those younger than 40), sex (21% in women versus 13% in men), and especially the occurrence of colonic perforation (44% for cases with perforation versus only 2% in those without). Of the 12 patients who died, 11 had suffered colonic perforation.(ABSTRACT TRUNCATED AT 250 WORDS)